This invention relates to lactase. Lactase or beta-galactosidase (E.C: 3.2.1.23) is an enzyme, which catalyzes the hydrolysis of lactose (a disaccharide) into its component monosaccharides glucose and galactose. Lactose is present in dairy products and more specifically in milk, skimmed milk, cream, ice cream, fermented milk products such as yogurt, many young cheeses and other dairy products. The breakdown of lactose occurs in the intestinal wall of juvenile mammals (among which are humans) by the natural presence of lactase. Only a small part of the adult population has not lost this property and can still digest lactose. The nutritional and functional problems caused by lactose in most adults are caused by a lack of lactase and are well known and described. Members of such populations cannot hydrolyze lactose, which in such cases passes into the large intestine where it results in dehydration, poor calcium absorption, flatulence, belching and cramps, and, in severe cases, even watery explosive diarrhea.
An important industrial application of lactase is in the production of lactose-hydrolyzed milk products for lactose intolerant individuals. Such hydrolyzed milk products include pasteurized milk, UHT-milk and milk reconstituted from all or part of its original constituents with or without intermediate processing steps such as protein hydrolysis. Treatment with lactase may be done prior to or after the heat-treatment of the milk. The lactase treatment may be done by adding the enzyme to the milk or to one of its lactose-containing constituents.
The solubility properties of lactose are such that it may lead to its crystallization when present at high concentration, leading to a sandy or gritty texture in dairy products such as condensed milk, evaporated milk, dry milk, frozen milk, ice cream, and in confectionary products with a high content of milk. Full or partial hydrolysis of lactose by lactase eliminates this problem, providing products with a homogeneous texture and as a result a higher consumer acceptance.
Another industrial application of lactase is to increase sweet taste in lactose containing products like milk or yoghurt. The hydrolysis of lactose in such products results in increased sweet taste as a result of the production of glucose, while the caloric value of the product does not increase. Conversely, the use of lactase may also decrease sugar addition in sweetened dairy products, without compromising the sweet taste.
Another industrial application of lactase is the hydrolysis of lactose products containing dairy components such as bread. Lactose is added in such products to enhance flavour, retain moisture, provide browning and improve toasting properties. Hydrolyzed lactose syrups are promising in terms of e.g. enhancing crust-colour development, improving flavour and aroma, modifying texture, extending shelf life and strengthening loaf structure.
Lactose hydrolysis by lactase in fermented milk products such as yoghurt will increase sweet taste. Also, when the lactase is added prior to the beginning of the fermentative process, it may increase the rate of acid development and thus reduce processing times. The lactase treatment of milk or milk-derived products such as whey makes such products suitable for application in animal feed and pet food for lactose intolerant animals such as cats. The lactose hydrolysis allows the manufacture of higher concentrated whey and at the same time prevents gut problems, similar to those described earlier for lactose-deficient patients. Lactose hydrolyzed whey is concentrated to produce a syrup containing 70-75% solids and is used as a food ingredient in ice cream, bakery and confectionary products.
Lactases have been described and isolated from a large variety or organisms, including micro-organisms. Lactase is often an intracellular component of micro-organisms like Kluyveromyces and Bacillus. Kluyveromyces and especially K. fragilis and K. lactis, and other yeasts such as those of the genera Candida, Torula and Torulopsis are a common source of yeast lactases, whereas B. coagulans, B. circulans or lactic acid bacteria are well known sources of bacterial lactases. Several commercial lactase preparations, derived from these organisms are available such as MAXILACT® (from K. lactis, produced by DSM, Delft, the Netherlands). These lactases are so called neutral lactases since they have a pH optimum between pH=6 and pH=8.
Although yeast neutral lactases are often used in industry to produce lactose-free or lactose-reduced dairy products, the cost-in-use for the enzyme treatment is often high. Main reasons for the relative high cost-in-use of the enzyme are:                In order to maintain hygienic conditions in the production plant the incubation is performed at low temperature. At this temperature the industrially used lactases are not very active and should be added at relative high dosage.        The currently used lactases are inhibited by its products, especially galactose, at later stages of the incubation with lactase. When products with a low residual lactose concentration are required, extra enzyme has to be added to compensate for reduction in activity due to galactose accumulation.        The currently used lactase has a relative low specific activity in milk which requires the use of a high enzyme dosage in application.Consequently, enzyme dosage and costs for producing lactose-reduced and lactose-free products are relative high.        
It is evident that there is a need for one or multiple lactase variant(s) capable of overcoming at least one of the above-mentioned disadvantages.